This invention relates to a method for heating room space of a building, comprising conveyance of heat from a district heating liquid to a heating liquid of heating circuits for heating the building and the ventilation air or the like. The invention also relates to an apparatus for heating room space of a building.
In district heating plants and boiler plants, the temperature of supply water conducted from the plant is usually 90.degree. . . . 110.degree. C., depending on the plant. The water required for the heating, ventilation and tap water of buildings is generally heated in a heat exchanger, the temperature of the water supplied therefrom to the building being normally 70.degree. . . . 90.degree. C. In a peak load situation, according to which heating networks are usually designed, the temperature of return water conducted from the building cannot normally be dropped below 40.degree. C. The temperature of the district heating return water is thus approximately 50.degree. C. when minimum costs are to be achieved. In view of the investment costs, pumpage rates, heat losses, etc., of district heating networks, it would be advantageous to drop the temperature of the return water even more, but the costs of heat exchangers would increase rapidly even with a small additional drop, as the temperature difference even in the present apparatuses is rather small, about 10.degree. C.
In conventional buildings, the proportion of ventilation in the heating energy consumption of the building is approximately 35 . . . 50%, depending on the type of building and the systems utilized in it. Both the heat losses of the building and the heat requirement of ventilation are directly proportional to the difference between indoor and outdoor temperature, i.e. the ratio between them is approximately constant. The overall heat balance encompasses, in addition, the internal heat evolution of the building (lighting, electric appliances, people, etc.) and hot tap water, which are both independent of outdoor temperature and have opposite effects. The proportion of ventilation varies thus very little with changes in the outdoor temperature.